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5674 KiB

Open AccessFeature PaperArticle

Porphyrin Cobalt(III) “Nitrene Radical” Reactivity; Hydrogen Atom Transfer from Ortho-YH Substituents to the Nitrene Moiety of Cobalt-Bound Aryl Nitrene Intermediates (Y = O, NH)

by Monalisa Goswami, Christophe Rebreyend and Bas De Bruin

Molecules 2016, 21(2), 242; https://doi.org/10.3390/molecules21020242 - 20 Feb 2016

Cited by 21 | Viewed by 9881

Abstract

In the field of cobalt(II) porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH) aryl azides in Co(II) porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT) from [...] Read more.

In the field of cobalt(II) porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH) aryl azides in Co(II) porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT) from the OH or NH₂ group in the ortho-position to the nitrene moiety of the key radical-intermediate was observed. This leads to formation of reactive ortho-iminoquinonoid (Y = O) and phenylene diimine (Y = NH) species. These intermediates convert to subsequent products in non-catalyzed reactions, as is typical for these free organic compounds. As such, the observed reactions prevent the anticipated cobalt-mediated catalytic radical-type coupling of the nitrene radical intermediates to alkynes or alkenes. Nonetheless, the observed reactions provide valuable insights into the reactivity of transition metal nitrene-radical intermediates, and give access to ortho-iminoquinonoid and phenylene diimine intermediates from ortho-YH substituted aryl azides in a catalytic manner. The latter can be employed as intermediates in one-pot catalytic transformations. From the ortho-hydroxy aryl azide substrates both phenoxizinones and benzoxazines could be synthesized in high yields. From the ortho-amino aryl azide substrates azabenzene compounds were obtained as the main products. Computational studies support these observations, and reveal that HAT from the neighboring OH and NH₂ moiety to the nitrene radical moiety has a low energy barrier. Full article

(This article belongs to the Special Issue Organic Azides)

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16507 KiB

Open AccessArticle

Improved Schmidt Conversion of Aldehydes to Nitriles Using Azidotrimethylsilane in 1,1,1,3,3,3-Hexafluoro-2-propanol

by Hashim F. Motiwala, Qin Yin and Jeffrey Aubé

Molecules 2016, 21(1), 45; https://doi.org/10.3390/molecules21010045 - 29 Dec 2015

Cited by 10 | Viewed by 7890

Abstract

The Schmidt reaction of aromatic aldehydes using a substoichiometric amount (40 mol %) of triflic acid is described. Low catalyst loading was enabled by a strong hydrogen-bond-donating solvent hexafluoro-2-propanol (HFIP). This improved protocol tolerates a broad scope of aldehydes with diverse functional groups [...] Read more.

The Schmidt reaction of aromatic aldehydes using a substoichiometric amount (40 mol %) of triflic acid is described. Low catalyst loading was enabled by a strong hydrogen-bond-donating solvent hexafluoro-2-propanol (HFIP). This improved protocol tolerates a broad scope of aldehydes with diverse functional groups and the corresponding nitriles were obtained in good to high yields without the need for aqueous work up. Full article

(This article belongs to the Special Issue Organic Azides)

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2315 KiB

Open AccessArticle

Synthesis of New 2-Halo-2-(1H-tetrazol-5-yl)-2H-azirines via a Non-Classical Wittig Reaction

by Ana L. Cardoso, Carmo Sousa, Marta S. C. Henriques, José A. Paixão and Teresa M. V. D. Pinho e Melo

Molecules 2015, 20(12), 22351-22363; https://doi.org/10.3390/molecules201219848 - 12 Dec 2015

Cited by 16 | Viewed by 5773

Abstract

The synthesis and reactivity of tetrazol-5-yl-phosphorus ylides towards N-halosuccinimide/TMSN₃ reagent systems was explored, opening the way to new haloazidoalkenes bearing a tetrazol-5-yl substituent. These compounds were obtained as single isomers, except in one case. X-ray crystal structures were determined for three [...] Read more.

The synthesis and reactivity of tetrazol-5-yl-phosphorus ylides towards N-halosuccinimide/TMSN₃ reagent systems was explored, opening the way to new haloazidoalkenes bearing a tetrazol-5-yl substituent. These compounds were obtained as single isomers, except in one case. X-ray crystal structures were determined for three derivatives, establishing that the non-classical Wittig reaction leads to the selective synthesis of haloazidoalkenes with (Z)-configuration. The thermolysis of the haloazidoalkenes afforded new 2-halo-2-(tetrazol-5-yl)-2H-azirines in high yields. Thus, the reported synthetic methodologies gave access to important building blocks in organic synthesis, vinyl tetrazoles and 2-halo-2-(tetrazol-5-yl)-2H-azirine derivatives. Full article

(This article belongs to the Special Issue Organic Azides)

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1240 KiB

Open AccessCommunication

Synthesis, Characterization and Reactions of (Azidoethynyl)trimethylsilane

by Klaus Banert, Manfred Hagedorn, Zhuang Wu and Xiaoqing Zeng

Molecules 2015, 20(12), 21328-21335; https://doi.org/10.3390/molecules201219770 - 01 Dec 2015

Cited by 7 | Viewed by 6236

Abstract

Synthesis of azido(trimethylsilyl)acetylene (6) was performed by treating the iodonium salt 5 with highly soluble hexadecyltributylphosphonium azide (QN₃) at −40 °C. Although this product is very unstable, it can nevertheless be trapped by the click reaction with cyclooctyne to [...] Read more.

Synthesis of azido(trimethylsilyl)acetylene (6) was performed by treating the iodonium salt 5 with highly soluble hexadecyltributylphosphonium azide (QN₃) at −40 °C. Although this product is very unstable, it can nevertheless be trapped by the click reaction with cyclooctyne to give the corresponding 1,2,3-triazole, and also directly characterized by ¹H- and ¹³C-NMR data as well as IR-spectra, which were measured in solution at low temperature and in the gas phase. The thermal or photochemical decay of azide 6 leads to cyano(trimethylsilyl)carbene. This is demonstrated not only by quantum chemical calculations, but also by the trapping reactions with the help of isobutene. Full article

(This article belongs to the Special Issue Organic Azides)

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2039 KiB

Open AccessArticle

Towards the Synthesis of Graphene Azide from Graphene Oxide

by Christian E. Halbig, Philipp Rietsch and Siegfried Eigler

Molecules 2015, 20(12), 21050-21057; https://doi.org/10.3390/molecules201219747 - 26 Nov 2015

Cited by 15 | Viewed by 7721

Abstract

In the last decades, organic azides haven proven to be very useful precursors in organic chemistry, for example in 1,3-dipolar cycloaddition reactions (click-chemistry). Likewise, azides can be introduced into graphene oxide with an almost intact carbon framework, namely oxo-functionalized graphene (oxo-G₁), [...] Read more.

In the last decades, organic azides haven proven to be very useful precursors in organic chemistry, for example in 1,3-dipolar cycloaddition reactions (click-chemistry). Likewise, azides can be introduced into graphene oxide with an almost intact carbon framework, namely oxo-functionalized graphene (oxo-G₁), which is a highly oxidized graphene derivative and a powerful precursor for graphene that is suitable for electronic devices. The synthesis of a graphene derivative with exclusively azide groups (graphene azide) is however still a challenge. In comparison also hydrogenated graphene, called graphene or halogenated graphene remain challenging to synthesize. A route to graphene azide would be the desoxygenation of azide functionalized oxo-G₁. Here we show how treatment of azide functionalized oxo-G₁ with HCl enlarges the π-system and removes strongly adsorbed water and some oxo-functional groups. This development reflects one step towards graphene azide. Full article

(This article belongs to the Special Issue Organic Azides)

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Review

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7253 KiB

Open AccessReview

Azidation in the Difunctionalization of Olefins

by Kai Wu, Yujie Liang and Ning Jiao

Molecules 2016, 21(3), 352; https://doi.org/10.3390/molecules21030352 - 16 Mar 2016

Cited by 103 | Viewed by 10962

Abstract

Organic azides are key motifs in compounds of relevance to chemical biology, medicinal chemistry and materials science. In addition, they also serve as useful building blocks due to their remarkable reactivity. Therefore, the development of efficient protocols to synthesize these compounds is of [...] Read more.

Organic azides are key motifs in compounds of relevance to chemical biology, medicinal chemistry and materials science. In addition, they also serve as useful building blocks due to their remarkable reactivity. Therefore, the development of efficient protocols to synthesize these compounds is of great significance. This paper reviews the major applications and development of azidation in difunctionalization of olefins using azide reagents. Full article

(This article belongs to the Special Issue Organic Azides)

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4134 KiB

Open AccessReview

Synthesis and Chemistry of Organic Geminal Di- and Triazides

by Andreas P. Häring and Stefan F. Kirsch

Molecules 2015, 20(11), 20042-20062; https://doi.org/10.3390/molecules201119675 - 06 Nov 2015

Cited by 36 | Viewed by 9573

Abstract

This review recapitulates all available literature dealing with the synthesis and reactivity of geminal organic di- and triazides. These compound classes are, to a large extent, unexplored despite their promising chemical properties and their simple preparation. In addition, the chemistry of carbonyl diazide [...] Read more.

This review recapitulates all available literature dealing with the synthesis and reactivity of geminal organic di- and triazides. These compound classes are, to a large extent, unexplored despite their promising chemical properties and their simple preparation. In addition, the chemistry of carbonyl diazide (2) and tetraazidomethane (105) is described in separate sections. Full article

(This article belongs to the Special Issue Organic Azides)

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860 KiB

Open AccessReview

Six-Membered Aromatic Polyazides: Synthesis and Application

by Sergei V. Chapyshev

Molecules 2015, 20(10), 19142-19171; https://doi.org/10.3390/molecules201019142 - 21 Oct 2015

Cited by 23 | Viewed by 9544

Abstract

Aromatic polyazides are widely used as starting materials in organic synthesis and photochemical studies, as well as photoresists in microelectronics and as cross-linking agents in polymer chemistry. Some aromatic polyazides possess high antitumor activity, while many others are of considerable interest as high-energy [...] Read more.

Aromatic polyazides are widely used as starting materials in organic synthesis and photochemical studies, as well as photoresists in microelectronics and as cross-linking agents in polymer chemistry. Some aromatic polyazides possess high antitumor activity, while many others are of considerable interest as high-energy materials and precursors of high-spin nitrenes and C₃N₄ carbon nitride nanomaterials. The use of aromatic polyazides in click-reactions may be a new promising direction in the design of various supramolecular systems possessing interesting chemical, physical and biological properties. This review is devoted to the synthesis, properties and applications of six-membered aromatic compounds containing three and more azido groups in the ring. Full article

(This article belongs to the Special Issue Organic Azides)

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